1. Field of the Invention
The present invention relates to earth formation analysis in general and, more particularly, to microwave spectrometry of an earth formation core and to surfactant testing.
2. Prior Art
Heretofore a method of analyzing in situ oil-brine saturation of samples of an earth formation in a laboratory were of the type described by R. W. Parsons, MICROWAVE ATTENUATION--A NEW TOOL FOR MONITORING SATURATIONS IN LABORATORY FLOODING EXPERIMENTS, Society of Petroleum Engineering Journal (August 1975, Volume 15, 302-309). However, these instruments are based upon a microwave frequency of about 21 GHz. Several difficulties arise from the high power level required at this frequency to penetrate the water-saturated rock slabs used in the experiments. Power levels are on the order of several hundred millawatts, far above established safe exposure limits. Because of this, adequate precaution must be taken to insure a safe working environment. The use of high power levels cause several instrumental complications.
To generate several hundred milliwatts of microwave power at 21 GHz, klystron sources are used which require specialized power supplies for stable operation and also requires considerable maintenance. Further since a wide range of power is transmitted through a core during a flooding experiment, precision attenuators are required to maintain the power level within the range limits of the detector. Isolators must be used to shield the klystron from reflective radiation. Tuners are employed to precisely match impedances from maximum power transfer efficiency. Microwave power is directed to and from the porous medium by lens-corrected directional horns. Transmitted power is detected by a thermocouple or crystal based power meter, converted to a voltage and passed to a logarithmic amplifier. The output is proportional to the water saturation of the core.
In addition to the undesirable expense and complexity of the aforementioned designs, practical application has been restricted to epoxy-coated flat slabs of Berea sandstone having typical dimensions of 2.54 cm thick, 10.2 cm wide and up to 122 cm long.
The present invention by utilizing a small cross-sectional area test core is capable of operating throughout the microwave frequency range at lower power level than Parsons and does not require the safety equipment nor the complex instrumentation required in the aforementioned Parsons apparatus. The present invention eliminates isolators and does not have to be tuned.